1. Field of the Invention
The present invention relates to a motor driving apparatus for controlling a rotation of a stepping motor, a control method therefor, control program therefor, a storage medium readable by a computer storing such control program, and an image forming apparatus such as a copying machine and the like having a recording paper conveying system including the stepping motor as a driving source.
2. Related Background Art
In recent years, in image forming apparatuses such as copying machines, there has been requested an image forming apparatus in which image formation can be performed at a higher speed with a compact construction. In order to permit the image formation at the higher speed with the compact construction, a position of a recording paper being conveyed must be grasped correctly. However, in the conventional techniques, a motor used as a driving source of a recording paper conveying system of an image forming apparatus is a DC motor, and there is dispersion in operations of clutches and solenoids constituting a conveying mechanism and, thus, there is dispersion in a sheet conveying distance. In high speed machines, since such dispersion becomes great, a stepping motor capable of determining a rotational angle correctly in accordance with the number of inputted pulses has been used.
A general method for rising-up the stepping motor will be explained hereinbelow.
A positional relationship between a stator and a rotor of the stepping motor in a non-excited condition that exciting electrical current is not applied to the stepping motor (for example, power OFF) is as shown in FIG. 1A. In this condition, the rotor is stopped at a most stabilized position by an influence of only a magnetic force. Thereafter, for example, upon initiation of a copying operation, when the electrical current is applied to the stepping motor to cause the exciting, as shown in FIG. 1B, a position where the rotor is electrically stabilized with respect to the rotor is established. In order to continue to rotate the motor, an exciting phase of the motor must be successively changed by driving clocks.
However, when the non-excited condition is transferred to the electrically stabilized condition, in order to correct the deviated positional relationship between the stator and the rotor, torque of the stepping motor is changed greatly by the magnetic force. While the torque is being changed, the exciting phase is switched by the driving clock, with the result that, if the rotor tries to rotate continuously, the motor will be out-of-phase.
As one of methods for preventing the out-of-phase, there is so-called pre-multi-rotation in which the motor is rotated for a predetermined time period upon power ON. The exciting phase is determined by the pre-multi-rotation, and the positional relationship between the stator and the rotor is stored in a storing device, so that the stepping motor can be rotated smoothly when the copying operation is started.
Further, as a second method, there is a method in which only exciting electrical current having predetermined phase is flown through the motor sufficiently before the motor is rotated, and, after the positional relationship between the stator and the rotor is stabilized and the fluctuation of torque is ceased, the rotation of the motor is started.
However, in the recording paper conveying system of the image forming apparatus using the stepping motor as the driving source, when the stepping motor is actually rotated by the above-mentioned pre-multi-rotation, if the recording paper exists on a sheet feed roller to be rotated thereby, the recording sheet is conveyed, with the result that sheet jam may occur.
Further, in compact and high speed image forming apparatuses, since a distance between a sensor for generating a motor driving start signal (and disposed in front of the sheet feed roller) and the sheet feed roller is limited and a time period from when the recording sheet is passed by the sensor to when the sheet reaches the sheet feed roller is short, the exciting cannot be effected sufficiently before the driving of the motor is started.
Further, regardless of the sensor, if the exciting electrical current is previously applied for a predetermined time period, since the current continues to flow through the motor, power consumption will increased.